A method and a device of the general type described supra is for example known from GB 2 377 362 A. They are essential in particular for the so called weight precise cutting since food strands with irregular shapes, typically naturally grown food strands, for example pork chop strands are typically cut into individual slices which shall have uniform masses. The requirement to produce identical package weights for the sale of the products is of interest for example in self service sections of super markets.
In the method disclosed in GB 2 377 362 A, a marking is generated on a surface of the food strand to be cut through four lasers respectively arranged offset by 90° in circumferential direction and oriented in a projection plane orthogonal to the feed direction. This marking is detected by three cameras, wherein two cameras are arranged above the conveyor belt elements separated by a transition gap (gap portion) and one camera is arranged below the conveyor belt elements. The three cameras and their optical axes are arranged within the same plane, this means the projection plane in which the marking is generated through the four lasers.
This system yields satisfactory results in a center portion of the food strand, in particular when the surface is relatively smooth and also facilitates continuous measuring and cutting operations with higher feed velocities and smaller offsets between the projection plane and the subsequent cutting plane with reasonable computing power. The known system, however, has a weakness when measuring end pieces and irregular surface contours, in particular including cavities extending into the food strand at a slant angle. In this case shadowing occurs in particular for irregular convex cambered end pieces and cavities with small curvature radii which prevent a reliable detection of the pattern generated by the lasers through the cameras.
DE 101 36809 A1 respectively using a light emitter and a camera furthermore also describes the technology for which the instant application provides an improvement. The emitter, for example a laser, projects light onto the food strand so that the reflection generates an optical edge contour on the food strand. The light is thus radiated on the food strand so that the contour extends perpendicular to a feed direction of the food strand. The edge contour can be subsequently captured by the camera and can be subsequently processed by a processor unit, wherein a cross sectional surface of the food strand can be determined. Knowing a mean density of the food strand facilitates computing which cutting thickness of a slice cut off from the food strand yields a precise predetermined mass.
Similar to this method WO 02/061368 A2 illustrates a device which also uses an emitter and a camera for determining a cross section surface of a food stand. This application relates in particular to the problem that a reliable determination of the edge contour or of the surface of the food strand is not easily possible in cases in which the food strand has a highly irregular structure as can be the case of strands of pork chops. Irregularities cause in particular the problem of shadowing particular portions as soon as the light emitted by the light emitter cannot reach every location of the cross section any more due to the irregular shape of the food strand so that the edge contour consequently “disappears” in these portions. Measuring errors and lack of precision of the masses of the particular slices come as a consequence. As a solution for this problem WO 02/061368 A2 proposes arranging mirrors around the food strand through which the food strand can be viewed from different viewing points. Thus, the mirrors are effective for the light emitted by the light emitter and also for the camera which shall capture the edge contour generated on the food strand.
An alternative option for precisely determining even complex cross section geometries and cross section surfaces of a food strand resulting therefrom is provided by the devices with the types IPM 3×300 and I-Cut 36 of the Marel hf. company. In particular the latter model uses three cameras instead of mirrors in order to avoid a shadowing of the edge contour projected with a laser on the food strand. Viewed in feed direction of the food strand two of the three cameras are positioned at a slanted lower position below the food strand while the third camera is arranged above the food strand. The “viewing directions” of the cameras are oriented in feed direction of the food strand, this means the cameras are arranged viewed in feed direction of the food strand in front of the edge contour generated by the light emitter and monitor the edge contour. By arranging three cameras about the food strand the edge contour on the food strand can be observed in a rather reliable manner, wherein shadowing and therefore imprecise cutting is reduced.
Though this device provides sufficient precision for some applications with respect to mass deviations of the particular slices of the food strand a safe prevention of shadowing of the edge contour which makes the edge contour invisible and not monitorable by the cameras cannot be safely provided by this device in all cases.
DE 600 332 T2 further discloses a cutting machine with automatic scanning of the food strand. Also in this machine measuring the cross sectional surface, this means computing disc thicknesses continuously during feeding and cutting operations is continuously provided. However, the product is pushed over thin horizontal support rods in the measuring device during feeding through feed fingers engaging a face. Generating the marking through two lasers and also detecting the marking through two cameras is thus performed without being impeded by conveyor belt elements which only leave a gap portion open between one another in order to reach the surface of the food strand from below. A marking laser and an associated camera are arranged above the support rods used as a support for the food strand and another marking laser including the associated camera is arranged below the support rod. The results of the measurement from the bottom side are flawed accordingly since the marking on the food strand is incomplete due to the plurality of support rods so that interpolation processes are required for the shadowed portions, which has a negative effect on precision. Based on the only two cameras furthermore imprecisions at the vertically aligned side surfaces are also only detectable incompletely.
Eventually EP 1 044 770 A1 and EP 1 046 478 A1 respectively disclose a method and a device for cutting particular components with predetermined weights from a piece of smoked ham. Measuring the food strand, in particular determining its cross sectional surface over its extension in feed direction is performed on a measuring table on which the product stands still during measuring. Thus, the product is supported according to EP 1 044 770 A1 by thin wires during measuring, whereas it is placed on a transparent glass plate according to EP 1 046 478 A1. In both cases the marking laser and also cameras are provided for detecting the marking on the top side of the ham, thus respectively plural marking lasers and cameras which are directed onto the food strand from above and also plural marking lasers and cameras which are directed onto the food strand from below. Thus, one respective marking laser (projector) and a camera interact as a pair. Since the food strand is standing still during measurement, there is sufficient time to process the plurality of images generated through a computer in order to determine the contour of the food strand. However, the known projector and camera technique and arrangement is not suitable for a method in which the measurement and evaluation of the measurement data obtained has to be continuously performed with uninterrupted feeding in order to be able to determine and adjust the required slice thickness in time before reaching the cutting plane.